Method for producing polymers

ABSTRACT

A process for the preparation of polymers is described, wherein at least one first ethylenically unsaturated monomer is subjected to a free radical polymerization in the presence of stable free radicals or sources of stable free radicals and of a compound having at least one free thiol group to give a polymer, and wherein the molar ratio of compound having a free thiol group to stable free radicals is from 0.05 to 1.1.  
     The polymerization rate is substantially increased by the compound having a free thiol group.

[0001] The present invention relates to a process for the preparation ofpolymers having a narrow molecular weight distribution and a polymerprepared by the process.

[0002] Usually, polymers prepared by free radical polymerization ofethylenically unsaturated monomers have the disadvantage that themolecular weight of the polymer chains increases nonlinearly with thepolymerization conversion and the polymer chains of the resultingpolymer do not have a uniform molecular weight. The polymer obtainableby free radical polymerization therefore usually has a highpolydispersity index PDI (PDI=M_(w)/M_(n), where M_(w) is the weightaverage molecular weight of the polymer and M_(n) is the number averagemolecular weight of the polymer. This is due on the one hand to thehalf-lives of the free radical initiators, which may be from a fewminutes to several hours. Consequently, the growth does not begin at thesame time for all polymer chains, and it is for this reason that chainshaving different chain lengths form during the reaction. On the otherhand, the growing polymer chains react with one another with combinationor disproportionation, which leads to termination of chain growth. Sincesuch termination reactions occur during the entire reaction time, thistoo leads to different chain lengths in the polymer.

[0003] In order to obtain polymers having a narrow molecular weightdistribution, the growth of the chain should begin as far as possible atthe same time for all polymer molecules and chain termination reactionsshould be suppressed.

[0004] WO 94/11412 describes a polymerization process for thepreparation of a thermoplastic resin, a mixture of free radicalinitiator, a stable free radical and at least one polymerizable monomerbeing heated. Polymers having a narrow polydispersity are obtained.TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) and PROXY(2,2,5,5-tetramethyl-1-pyrrolidinyloxy) and derivatives thereof areproposed as stable free radical.

[0005] Further processes for the control of free radical polymerization,i.e. for the free radical polymerization in the presence of stable freeradicals, are described in EP-A-0 735 052, U.S. Pat. No. 5,322,912, U.S.Pat. No. 5,412,047 and GB 1,124,009.

[0006] However, the processes described in said publications have thedisadvantage that the polymerization takes place only very slowly andwith unsatisfactory conversion in the presence of the stable freeradicals.

[0007] EP-A-0 735 052 describes a polymerization process for thepreparation of thermoplastic resins, in which specific sulfonic acidsalts are concomitantly used for increasing the polymerization rate ofthe controlled free radical polymerization. 2-Fluoro-1-methylpyridiniump-toluenesulfonate is particularly preferably used. The sulfonic acidsalts described are however not directly available and, owing to theirfluorine content, are undesired in certain applications.

[0008] It is an object of the present invention to provide analternative process for the preparation of polymers having a narrowmolecular weight distribution, which process permits a higher reactionrate and higher conversions compared with known controlled free radicalpolymerizations.

[0009] We have found that this object is achieved by a process for thepreparation of polymers, wherein at least one ethylenically unsaturatedmonomer is subjected to a free radical polymerization in the presence ofstable free radicals or sources of free radicals and of a compoundhaving at least one free thiol group to give a polymer, and wherein themolar ratio of compound having free thiol group to stable free radicalsis from 0.05 to 1.1.

[0010] Surprisingly, it has been found that a substantial increase inthe polymerization rate can be achieved by adding compounds which haveat least one free thiol group, molecular weight control simultaneouslybeing maintained. The compound having at least one free thiol group isused in an amount such that the molar ratio of compound having a freethiol group to stable free radical is from 0.05 to 1.1, preferably from0.05 to 0.8, in particular from 0.1 to 0.7. At an amount below saidrange, no significant effect which increases the polymerization rate isobserved. At an amount above said range no further rate increase occurs,and polymers having undesirably low molecular weights are obtained.

[0011] The polymers prepared by the novel process generally have apolydispersity index of from 1.1 to 5, preferably from 1.2 to 3.5, inparticular from 1.3 to 2.5.

[0012] For carrying out the novel process, a reaction mixture whichcontains a stable free radical or a source of a stable free radical, atleast one ethylenically unsaturated monomer and a compound having atleast one free thiol group and, if required, a free radical initiatorand, if required, solvents and/or conventional polymerization assistantsis expediently heated to a high reaction temperature, for example from40 to 200° C., in particular from 60 to 150° C. After reaction andcooling are complete, the polymer can be isolated and, if required,washed and dried. If the free radical formers described in more detailbelow are used as a source of the stable free radicals, the addition ofa separate free radical initiator is superfluous. Alternatively, thefree radical polymerization can also be thermally initiated in theabsence of free radical initiators, in particular when vinylaromaticmonomers, such as styrene, are used. Of course, mixtures ofethylenically unsaturated monomers may also be used.

[0013] The process is also suitable for the preparation of blockcopolymers. For this purpose, at least one second ethylenicallyunsaturated monomer is subjected to a free radical polymerization in thepresence of the polymer obtained above. In a suitable procedure, thesecond ethylenically unsaturated monomer, which as a rule is differentfrom the first ethylenically unsaturated monomer, is added to thepolymer, which may have been isolated, if required with addition offresh amounts of free radical initiator and free stable radicals, andthe mixture is heated for polymerization. After cooling, a blockcopolymer is isolated and, if required, is washed and dried. Here, asecond ethylenically unsaturated monomer is also to be understood asmeaning a monomer mixture which is different from the firstethylenically unsaturated monomer with respect to the constitutivemonomers or composition.

[0014] In order to obtain higher block copolymers, a third monomer maybe added after polymerization of the second monomer and thepolymerization may be carried out in the same manner. The isolation ofthe polymers formed as intermediates is advisable when a very highpurity, well defined block limits and/or high homogeneity within theblocks are desired.

[0015] Suitable free radical initiators for the polymerization are inprinciple all compounds which are capable of initiating a free radicalpolymerization. Suitable free radical initiators are, for example,peroxides, hydroperoxides, peroxodisulfates, percarbonates,peroxoesters, hydrogen peroxide and azo compounds. Examples ofinitiators are hydrogen peroxide, dibenzoyl peroxide, dicyclohexylperoxodicarbonate, dilauroyl peroxide, methyl ethyl ketone peroxide,di-tert-butyl peroxide, acetylacetone peroxide, tert-butylhydroperoxide, cumyl hydroperoxide, tert-butyl perneodecanoate,tert-amyl perpivalate, tert-butyl perpivalate, tert-butylperneohexanoate, tert-butyl perbenzoate, lithium, sodium, potassium andammonium peroxodisulfate, azoisobutyronitrile,2,2-azobis(2-amidinopropane) dihydrochloride,2-(carbamoylazo)isobutyronitrile and 4,4-azobis(4-cyanovaleric acid).The free radical initiator may be both oil-soluble and water-soluble andare adapted to the chosen polymerization medium and to the chosenpolymerization temperature in a manner known per se.

[0016] Suitable monomers polymerizable by the novel process are allthose which have at least one ethylenically unsaturated group. Themonomers may be used individually or as mixtures of one another. Thesemonomers include olefins, in particular a-olefins, e.g. ethylene andpropylene, cycloalkenes, such as cyclohexene or norbornene,vinylaromatic monomers, such as styrene, α-methylstyrene,o-chlorostyrene or vinyltoluenes, 1,1-diphenylethylene and cis- and/ortrans-stilbene, it being possible for the phenyl rings to have one ortwo substituents selected from nitro, hydroxyl, halogen, C₁-C₄-alkyl,C₁-C₄-alkoxy, cyano and sulfonate, and vinyl halides and vinylidenehalides, such as vinyl chloride or vinylidene chloride, esters of vinylalcohol and monocarboxylic acids of 1 to 12 carbon atoms, such as vinylacetate, vinyl propionate, vinyl n-butyrate or vinyl laurate, esters ofallyl alcohol with monocarboxylic acids of 1 to 12 carbon atoms, such asallyl acetate, allyl propionate, allyl n-butyrate and allyl laurate,esters of α,β-monoethylenically unsaturated mono- and dicarboxylic acidsof, preferably, 3 to 6 carbon atoms, in particular acrylic acid,methacrylic acid, maleic acid, fumaric acid and itaconic acid, withalkanols of in general 1 to 12, preferably 1 to 8, in particular 1 to 4,carbon atoms, especially methyl, ethyl, n-butyl, isobutyl, tert-butyland 2-ethylhexyl acrylate and methacrylate, dimethyl maleate or n-butylmaleate, nitriles of α,β-monoethylenically unsaturated carboxylic acids,such as acrylonitrile and methacrylonitrile, and conjugated C₄- toC₈-dienes, such as 1,3-butadiene and isoprene. Furthermore,α,β-monoethylenically unsaturated mono- and dicarboxylic acids of 3 to 6carbon atoms, their anhydrides and their amides, e.g. acrylic acid,methacrylic acid, maleic acid, fumaric acid and itaconic acid; maleicanhydride; acrylamide and methacrylamide, N-methylacrylamide,N-ethylacrylamide, N-isopropylacrylamide and N,N′-dimethylacrylamide,and furthermore vinylsulfonic acid and its water-soluble salts, andN-vinylpyrrolidone, are suitable. This also applies to those monomerswhich have a functional group, e.g. an epoxy, hydroxyl, ureido orN-methylol group. Examples of these are glycidyl (meth)acrylate,hydroxyalkyl (meth)acrylates, aminoalkyl (meth)acrylates,N-alkylolamides of α,β-monoethylenically unsaturated carboxylic acids of3 to 10 carbon atoms and their esters with alkanols of 1 to 4 carbonatoms.

[0017] Preferably used monomers are styrene, butadiene, acrylonitrile,n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, n-butylmethacrylate and tert-butyl methacrylate and mixtures thereof.

[0018] Compounds suitable according to the invention and having at leastone free thiol group are preferably those of the formula (I)

[0019] where

[0020] R¹, R², and R³, independently of one another, are each hydrogen,alkyl, aryl, aralkyl, cycloalkyl, heterocyclyl or a group -Y-Z, where

[0021] Y is selected from a single bond, linear or branched alkylene,which may be interrupted by one or more non-neighboring oxygen atoms, orarylene, which is unsubstituted or substituted by C₁-C₄-alkyl,C₁-C₄-alkoxy or halogen, and

[0022] Z is selected from the following functional groups: —OR⁴, —NR⁴R⁵,—N+R⁴R⁵R⁶, —C(O)—R⁴, C(O)—NR⁴R⁵, —OC(O)—OR⁴, —OC(O)—NR⁴R⁵,—N(R⁶)—C(O)—R⁴, —N(R⁶)—C(O)—OR⁴, —N(R⁶)—C(O)—NR⁴R⁵, —SR⁴, —S(O)—R⁴,—S(O)₂—R⁴, —O—S(O)₂—OR⁴, Si(R⁷)₃, —O—Si(R⁷)₃, —S(O)₂—NR⁴R⁵, —P(O)(OR⁴)₂,—P(O)(NR⁴R⁵)₂, —O—P(O)R⁴(OR⁵), —Si(OR⁷)₃, —OSi(OR⁷)₃, —CN, —OCN, —SCN,—NO₂ or halogen, and, in the case of acidic functional groups, also thealkali metal, alkaline earth metal or ammonium salts and, in the case ofbasic groups, also the acid addition salts, and where R⁴, R⁴, R⁶ and R⁷,independently of one another, are each hydrogen, alkyl, aryl, aralkyl,alkylcarbonyl or arylcarbonyl; or

[0023] R¹ and R², together with the carbon atom to which they arebonded, are a cycloalkyl radical which may have at least one of theabovementioned functional groups -Y-Z, a double bonded oxygen or, ifrequired, oxygen, nitrogen or sulfur as a heteroatom;

[0024] or R¹ and R², together with the carbon atom to which they arebonded, are a carbonyl function or an imino function which isunsubstituted or substituted by alkyl, aryl or aralkyl, or

[0025] R¹, R² and R³, together with the carbon atom to which they arebonded, are an aryl radical which may have at least one of theabovementioned groups -Y-Z, or

[0026] R¹, R² and R³ together are a heterocyclic radical.

[0027] “Alkyl” is preferably C₁-C₂₀-alkyl; “aryl” is preferablyC₆-C₁o-aryl, in particular phenyl; “aralkyl” is preferablyphenyl-C₁-C₈-alkyl, in particular benzyl or phenethyl; “cycloalkyl” ispreferably C3-C₈-cycloalkyl, in particular cyclopentyl and cyclohexyl;“heterocyclyl” is preferably an aromatic radical having a five-memberedring, in which 1, 2, 3 or 4 atoms may be different from carbon and areselected, for example, from O, S and/or N.

[0028] Preferably, the compound having at least one free thiol group isselected from alkyl mercaptans, aminoalkane thiols and their mono- anddi-N-C₁-C₄-alkyl derivatives; aromatic aminothiols and their mono- anddi-N-C₁-C₄-alkyl derivatives; aliphatic and aromatic mercaptocarboxylicacids, mercaptodicarboxylic acids and aminomercaptocarboxylic acids,their N-alkyl, N-aryl or N-aralkyl derivatives or their N,N-dialkyl,N,N-diaryl or N,N-bis(aralkyl) derivatives, the esters of saidcarboxylic acids with aliphatic, aromatic or araliphatic alcohols;aromatic and aliphatic mercapto alcohols and esters of the mercaptoalcohols with C₁-C₁₀-alkanecarboxylic acids, C₆-C₂₀-arylcarboxylic acidsor C₇-C₂₀-aralkylcarboxylic acids; mercaptodialkyl ketones;mercaptoalkylaryl ketones; mercaptoalkane- and mercaptoarylsulfonicacids and their alkali metal, alkaline earth metal and ammonium salts;thiourea, which is unsubstituted or substituted on one or both nitrogenatoms by alkyl, aryl, aralkyl, alkylcarbonyl or arylcarbonyl;thiosemicarbazide which is unsubstituted or substituted on the aminenitrogen by alkyl, aryl, aralkyl, alkylcarbonyl or arylcarbonyl;mercapto-substituted nitrogen heterocycles, includingmercapto-substituted imidazole, imidazoline, thiazole, thiazoline,triazole, thiadiazole and oxazole, which are unsubstituted orsubstituted by amino, halogen, alkyl or aryl and/or have a fused,unsubstituted or substituted benzene ring; aliphatic and aromaticdicarboxylic acids and their amides, N-alkylamides and N-arylamides;mercaptoalkyltrialkoxysilanes.

[0029] The compound having at least one free thiol group is selected inparticular from C₁-C₂₀-alkyl mercaptans, preferably C₄-Cl₈-alkylmercaptans, such as butanethiol or tert-dodecyl mercaptan or n-dodecylmercaptan, 2-aminoethanethiol, N-methyl-, N,N-dimethyl-, N-ethyl- andN,N-diethyl-2-aminoethanethiol, 2-, 3- and 4-aminothiophenol,2-mercaptoacetic acid, 2-mercaptopropionic acid, 2-mercaptoisobutyricacid, 2-mercaptosuccinic acid, 2-, 3- and 4-mercaptobenzoic acid,2-amino-3-mercapto-3-methylbutanoic acid, the methyl, ethyl and phenylesters of said carboxylic acids, 2-hydroxyethanethiol, 2- and3-hydroxypropanethiol, 2- and 4-hydroxybutanethiol,2-mercaptobutane-1,4-diol, a-thioglycerol, 2-hydroxycyclopentanethiol,2- and 4-mercaptophenol, 2-mercaptoethanesulfonic acid, 2- and3-mercaptopropanesulfonic acid, 2- and 4-mercaptobutanesulfonic acid andthe alkali metal, alkaline earth metal or ammonium salts of the saidsulfonic acids, 1-mercaptoacetone, phenacylthiol,4-mercaptoacetophenone, 4-mercaptobenzophenone, thiourea, N-methyl-,N-ethyl-, N-alkyl-, N-acetyl- and N-phenylthiourea, N,N-dimethyl-,N,N-diethyl-, N,N-diisopropyl-, N,N-di-n-butyl- andN,N-diphenylthiourea, thiosemicarbazide, 4-methyl-, 4-ethyl- and4-phenylthiosemicarbazide, mercaptothiadiazole,2-amino-5-mercaptothiadiazole, thiazoline-2-thiol, imidazoline-2-thiol,3-amino-5-mercaptotriazole, 2-mercaptobenzimidazole,2-mercaptobenzoxazole and 2-mercaptobenzothiazole, thioacetic acid,thiopropionic acid, thiobenzoic acid, thioacetamide, thiobenzamide,3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane.Owing to their availability, C₄-C₁₈-alkyl mercaptans are generallypreferred.

[0030] Stable free radicals may be added to the reaction mixture as suchor may be produced from free radical formers in the reaction mixture.Stable free radicals are usually not capable of initiating a freeradical polymerization of monomers. However, these compounds can controlthe growth of a polymer by reversibly blocking the chain end of saidpolymer, since in the steady state only a small number of free radicalchain ends are present in the reaction mixture, with the result that theprobability of irreversible chain termination reactions by combinationor disproportionation is reduced. Such stable free radicals which may beused for controlling free radical polymerization are known to a personskilled in the art.

[0031] The stable free radical or the source of stable free radicalshould be present in the reaction mixture in an amount of from 10⁻⁶ to10, in particular from 10⁻⁴ to 5, mol % based on the molar amount ofethylenically unsaturated monomers.

[0032] If the polymerization is initiated by free radical initiators,the molar ratio of stable free radical or of the source of stable freeradicals to free radical initiator is chosen in general to be from 0.1to 10, preferably from 0.5 to 5, in particular from 0.8 to 4.

[0033] Particularly suitable stable free radicals are free N-oxylradicals. They can be described, for example, by the following formula:

[0034] where R^(a) and R^(b) are organic radicals which may be linked toone another, the sum of the molecular weights of R^(a) and R^(b) beingmore than 15, preferably more than 28.

[0035] Suitable N-oxyl radicals have, for example, the followingstructures:

[0036] where R are identical or different alkyl, cycloalkyl, aralkyl oraryl radicals of up to 24 carbon atoms, it being possible for geminal Rradicals also to be linked in pairs to form a ring system, and X, Y andZ, independently of one another, are each CR′₂, CR′OH, CR′(COOH), O, NR,S, SO₂, CO or a chemical bond, with the proviso that not more than oneradical X, Y or Z is O or S and not more than one radical X, Y or Z is achemical bond. R′ is hydrogen or an alkyl, cycloalkyl, aralkyl or arylradical of up to 24 carbon atoms. For example, R is C₁- to C₂₀-alkyl, inparticular C₁- to C₈-alkyl, C₅- or C6-cycloalkyl, benzyl or phenyl.X-Y-Z is, for example, —(CH₂)₂— or —(CH₂)₃—, CH₂—CH(OH)—CH₂—, —CH₂—CO—O—or —CH₂—O—.

[0037] Furthermore, N-oxyl compounds having aromatic substituents, suchas the following structures, are also suitable

[0038] where the aromatic rings in each case may also carry from 1 to 3inert substituents, e.g. C₁- to C₄-alkyl, C₁- to C₄-alkoxy, ester, amideor cyano.

[0039] Advantageously used N-oxyl radicals are those which are derivedfrom cyclic amines, for example from piperidine or pyrrolidine compoundswhich may carry further heteroatoms, such as nitrogen, oxygen or sulfur,in the ring, this heteroatom not being in the neighboring position tothe amine nitrogen. The steric hindrance is provided by substituents inboth neighboring positions to the amine nitrogen, suitable substituentsbeing hydrocarbon radicals, which replace all 4 hydrogen atoms of thea-CH₂ groups. Examples of substituents are phenyl, C₃- to C₆-cycloalkyl,benzyl and in particular C₁- to C₆-alkyl, it being possible for thealkyl radicals bonded to the same a-carbon atom also to be bonded to oneanother to form a 5- or 6-membered ring. Preferably used N-oxyls aresterically hindered amine derivatives of 2,2,6,6-tetraalkylpiperidine.

[0040] Preferred N-oxyl compounds are those of the formula (II) or (IIa)

[0041] where

[0042] R⁸ and R⁹, independently of one another, are each C₁- to C₄-alkylor phenyl, or R⁸ and R⁹ together with the carbon atom to which they arebonded are a 5- or 6-membered, unsubstituted or substituted, saturatedhydrocarbon ring which may be bridged by C₁- or C₂-alkylene or fusedwith a further 5- or 6-membered hydrocarbon ring and may contain 1 or 2heteroatoms, selected from O, S and N, and 1 or 2 keto groups,

[0043] R¹⁰ is hydrogen, hydroxyl, amino, SO₃M, OSO₃M, P0₃M, OPO₃M₂, COOMor one of the following radicals

[0044]  where M is hydrogen or an alkali metal, preferably Li, Na or K,

[0045] R¹¹ is hydrogen, C₁- to C₄-alkyl or C₁- to C₄-alkoxy, or

[0046] R¹⁰ and R¹¹ together are oxygen or NOH, or

[0047] R¹⁰ and R¹¹, together with the carbon atom to which they arebonded, form a 5- or 6-membered, unsubstituted or substituted, saturatedring which may contain 1 or 2 heteroatoms, selected from O, S and N, and1 or 2 keto groups,

[0048] R¹² is C₁- to C₁₂-alkyl, C₂- to C₁₂-alkenyl, C₆- to C₁₂-aryl orC₇-to C₁₄-aralkyl,

[0049] Q is a m-valent organic radical linked via a carbon, oxygen orsulfur and preferably of 2 to 10 000, in particular 4 to 2 000, atoms,

[0050] m is 2 to 100, preferably 2 or 3, and

[0051] q is 1 to 10.

[0052] R⁸ and R⁹ may be Cl- to C₄-alkyl groups, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl ortogether may form a tetra- or pentamethylene group. Preferably, R⁸ andR⁹ are each methyl.

[0053] Preferred radicals Q are, for example, the following radicals

[0054] where

[0055] R¹³ is C₁- to C₁₂-alkyl, preferably C₁- to C₄-alkyl,

[0056] R¹⁴ is hydrogen or C₁- to C₁₂-alkyl, preferably hydrogen or C₁-to C₄-alkyl, and

[0057] x is 1 to 12.

[0058] Further suitable N-oxyls are also oligomeric or polymericcompounds which have a polysiloxane as the polymer main chain and aresubstituted in the side chain by N-oxyl groups which are derived from2,2,6,6-tetraalkylpiperidine. A preferably used N-oxyl group is2,2,6,6-tetramethylpiperidin-N-oxyl. Preferred nitroxyl compounds arethe following:

[0059] 1-oxyl-2,2,6,6-tetramethylpiperidine,

[0060] 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol,

[0061] 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one,

[0062] 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl acetate,

[0063] 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl 2-ethylhexanoate,

[0064] 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate,

[0065] 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl benzoate,

[0066] 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl (4-tert-butyl)benzoate,

[0067] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate,

[0068] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipate,

[0069] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate,

[0070] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) n-butylmalonate,

[0071] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate,

[0072] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) isophthalate,

[0073] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate,

[0074] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)hexahydroterephthalate,

[0075] N,N′-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipamide,

[0076] N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)caprolactam,

[0077] N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)dodecylsuccinimide,

[0078]N,N′-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-N,N′-bisformyl-1,6-diaminohexane,

[0079] 4,4′-ethylenebis(1-oxyl-2,2,6,6-tetramethylpiperazin-3-one),tris(2,2,6,6-tetramethyl-1-oxylpiperidin-4-yl) phosphite

[0080] 4-hydroxy-2,6-diphenyl-2,6-dimethyl-1-oxylpiperidine,

[0081] 4-carboxy-2,2,6,6-tetramethyl-1-oxylpiperidine,

[0082] 4-carboxy-2,6-diphenyl-2,6-dimethyl-1-oxylpiperidine,

[0083] 3-carboxy-2,2,5,5-tetramethyl-1-oxylpyrrolidine,

[0084] 3-carboxy-2,5-diphenyl-2,5-dimethyl-1-oxylpyrrolidine, thesodium, ammonium or potassium salt of the sulfuric monoester of4-hydroxy-2,2,6,6-tetramethyl-1-oxylpiperidine,

[0085] 5,5-dimethyl-3-spirocyclopentylmorphol-2-on-4-oxyl,

[0086] 5,5-dimethyl-3-spirocyclohexylmorphol-2-on-4-oxyl,

[0087] 5,5-dimethyl-3-spirocyclopentylmorpholin-4-oxyl,

[0088] 5,5-dimethyl-3-spirocyclohexylmorpholin-4-oxyl,

[0089] di-tert-butylnitroxyl,

[0090] N-tert-butyl-1-diethylphosphono-2,2-dimethylpropylnitroxyl and

[0091] N-tert-butyl-1-phenyl-2-methylpropylnitroxyl.

[0092] Suitable sources of stable free radicals are free radical formerswhere a stable free radical forms as a fragment as a result of homolyticcleavage, for example by thermolysis, of a chemical bond. A carbonradical which is suitable as a free radical initiator of thepolymerization reaction is preferably formed as the other fragment.

[0093] Preferred C radicals are the fragments of conventionalpolymerization initiators, e.g. methyl, ethyl, cyclohexyl, octyl,C(CN)(CH₃)₂—, CHPhCH₃— or CH(CH₃)COOR—(R═C₁-C₄-alkyl) radicals. For anoligomeric or polymeric chain, the carbon radical may furthermoreconsist of units of ethylenically unsaturated monomers. The free radicalformer can be prepared by heating stable free radicals with apolymerization initiator in the presence or absence of a small amount ofethylenically unsaturated monomers.

[0094] Emulsifiers or protective colloids may be present. Anionic,nonionic, cationic and amphoteric emulsifiers are suitable. Anionicemulsifiers, for example alkylbenzenesulfonic acid, sulfonated fattyacids, sulfosuccinates, fatty alcohol sulfates, alkylphenol sulfates andfatty alcohol ether sulfates, are preferred. The nonionic emulsifiersused may be, for example, alkylphenol ethoxylates, fatty acidethoxylates, alkanolamide methoxylates, alkanolamide ethoxylates, EO/POblock copolymers and alkylpolyglucosides. The cationic or amphotericemulsifiers used are, for example, quaternized aminoalkoxylates,alkylbetaines, alkylamidobetaines and sulfobetaines. Typical protectivecolloids are, for example, cellulose derivatives, polyethylene glycol,polypropylene glycol, copolymers of ethylene glycol and propyleneglycol, polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, starchand starch derivatives, dextran, polyvinylpyrrolidone,polyvinylpyridine, polyethyleneimine, polyvinylimidazole,polyvinylsuccinamide, polyvinyl-2-methylsuccinimide,polyvinyl-1,3-oxazolid-2-one and polyvinyl-2-methylimidazoline.

[0095] The novel process can be carried out as a solution, mass,suspension, precipitation, emulsion, miniemulsion or microemulsionpolymerization, in particular in an aqueous medium. The process can alsobe carried out as an inverse free radical emulsion polymerization.Suitable solvents for a solution polymerization procedure are, forexample, aliphatic or aromatic hydrocarbons, such as cyclohexane,methylcyclohexane, toluene, ethylbenzene or the xylenes. The novelprocess is carried out in a manner known per se to a person skilled inthe art. Solution, mass and miniemulsion polymerization methods aregenerally preferred.

[0096] The reaction temperature is chosen to be from 40 to 200° C.,preferably from 60 to 150° C. Suitable reaction times are from 30minutes to 60 hours.

[0097] The examples which follow illustrate the invention.

EXAMPLE 1

[0098] The amounts of 2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO),tert-dodecyl mercaptan (t-DMC) and dibenzoyl peroxide (BPO) stated inthe table below were dissolved in 360 g of styrene. 1 000 ml ofcyclohexane were added to the mixture and the latter was then heated to95° C. The sample was kept at this temperature for one hour and thenheated to 130° C. The samples were kept at 130° C. for the time statedin the table. Thereafter, the samples were cooled to room temperature,precipitated in an excess of methanol, collected by filtration, washedseveral times with methanol and dried at 80° C. under reduced pressure.The table shows the conversion, the weight-average molecular weight(M_(w)), the number-average molecular weight (M_(n)) and thepolydispersity (PDI) of the polymer obtained. TABLE TEM- Con- PO BPOt-DMC Time version M_(n) M_(w) [g] [g] [g] [h] [%] [g/mol] [g/mol] PDI 10.656 0.855 0.25 4 21.8 21200 28600 1.35 6 28.4 25200 35900 1.43 23 57.830900 51400 1.67 2 0.656 0.855 0.50 4 31 15700 22000 1.40 6 38.6 2060030600 1.49 23 64.5 23300 36800 1.58 3 0.656 0.855 1.00 4 30.8 1840031100 1.69 6 38.6 19200 34600 1.81 23 64.5 21800 42500 1.95 4 0.6560.855 1.70 4 32.9 n.d. n.d. 6 38.9 5 0.656 0.855 4.25 4 31.3 n.d. n.d. 641.1 6 0.656 0.855 0   5 0 — — —

[0099]FIG. 1 shows the conversion in % after 4 hours at 130° C. andafter 6 hours at 130° C. as a function of the molar ratio oftert-dodecyl mercaptan to TEMPO. As is evident from FIG. 1, nodeterminable conversion is observed without addition of tert-dodecylmercaptan. On addition of tert-dodecyl mercaptan in amounts such thatthe molar ratio of tert-dodecyl mercaptan to TEMPO is from 0.05 to 1.1,a substantial increase in the polymerization rate is observed. The useof larger amounts of tert-dodecyl mercaptan leads to no further increasein the polymerization rate.

EXAMPLE 2

[0100] 4-Hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl (4-OH-TEMPO) (0.82g) was dissolved in water (350 g). Benzoyl peroxide (75% strength inwater; 1.19 g), hexadecane (4.8 g), Lumiten I-RA(bisisooctylsulfosuccinate sodium salt; 50% strength in water; 4.8 g)and tert-dodecyl mercaptan (0.75 g) were added to a mixture of styrene(84.4 g) and n-butyl acrylate (155.7 g). The monomer mixture was addedto the aqueous solution of 4-OH-TEMPO and emulsified by means ofultrasonic treatment (5 minutes at a setting of 25% and a further 20minutes at 100%). After the emulsification, further emulsifier(Cl₅-alkanesulfonate sodium salt; 40% strength in water; 12 g) in water(10 g) was added. The emulsion was introduced into a pressure-resistantpolymerization vessel, the vessel was closed and the emulsion was heatedat 130° C. for 7 hours. Thereafter, the emulsion was cooled, theconversion was determined gravimetrically and the isolated polymer wasanalyzed by GPC. Conversion 86%; number-average molecular weight 33 000g/mol, polydispersity 1.9.

COMPARATIVE EXAMPLE 3

[0101] Example 2 was repeated, except that the monomer mixture containedno tert-dodecyl mercaptan. Conversion 44%; number-average molecularweight 23 000 g/mol; polydispersity 1.6.

We claim:
 1. A process for the preparation of polymers, wherein at leastone first ethylenically unsaturated monomer is subjected to a freeradical polymerization in the presence of stable free radicals orsources of stable free radicals and of a compound having at least onefree thiol group to give a polymer, and wherein the molar ratio ofcompound having a free thiol group to stable free radicals is from 0.05to 1.1.
 2. A process as claimed in claim 1, wherein at least one secondethylenically unsaturated monomer is subjected to a free radicalpolymerization in the presence of the polymer of the first ethylenicallyunsaturated monomer to give a block copolymer.
 3. A process as claimedin claim 1 or 2, wherein the molar ratio of compound having a free thiolgroup to stable free radicals is from 0.05 to 0.8.
 4. A process asclaimed in any of the preceding claims, wherein the compound having afree thiol group is selected from compounds of the formula (I)

where R¹, R², and R³, independently of one another, are each hydrogen,alkyl, aryl, aralkyl, cycloalkyl, heterocyclyl or a group -Y-Z, where Yis selected from a single bond, linear or branched alkylene, which maybe interrupted by one or more non-neighboring oxygen atoms, or arylene,which is unsubstituted or substituted by C₁-C₄-alkyl, C₁-C₄-alkoxy orhalogen, and Z is selected from the following functional groups: —OR⁴,—NR⁴R⁵, —N+R⁴R⁵R⁶, —C(O)—R⁴, C(O)—NR⁴R⁵, —OC(O) —OR⁴, —OC(O)—NR⁴R⁵,—N(R⁶) —C(O)—R⁴, —N(R⁶)—C(O)—OR⁴, —N(R⁶)—C(O)—NR⁴R⁵, —SR⁴, —S(O)—R⁴,—S(O)₂—R⁴, —O—S(O)₂—OR⁴, Si(R⁷)₃, —O—Si(R⁷)₃, —S(O)₂—NR⁴R⁵, —P(O)(OR⁴)₂,—P(O)(NR⁴R⁵)₂, —O—P(O)R⁴(OR⁵), —Si(OR⁷)₃, —OSi(OR⁷)₃, —CN, —OCN, —SCN,—NO₂ or halogen, and, in the case of acidic functional groups, also thealkali metal, alkaline earth metal or ammonium salts and, in the case ofbasic groups, also the acid addition salts, and where R⁴, R⁴, R⁶ and R⁷,independently of one another, are each hydrogen, alkyl, aryl, aralkyl,alkylcarbonyl or arylcarbonyl; or R¹ and R², together with the carbonatom to which they are bonded, are a cycloalkyl radical which may haveat least one of the abovementioned functional groups -Y-Z, a doublebonded oxygen or, if required, oxygen, nitrogen or sulfur as aheteroatom; or R¹ and R², together with the carbon atom to which theyare bonded, are a carbonyl function or an imino function which isunsubstituted or substituted by alkyl, aryl or aralkyl, or R¹, R² andR³, together with the carbon atom to which they are bonded, are an arylradical which may have at least one of the abovementioned groups -Y-Z,or R¹, R² and R³ together are a heterocyclic radical.
 5. A process asclaimed in any of the preceding claims, wherein the compound having atleast one free thiol group is selected from alkyl mercaptans,aminoalkane mercaptans, aminoalkanethiols and their mono- anddi-N-C₁-C₄-alkyl derivatives; aromatic aminothiols and their mono- anddi-N-C₁-C₄-alkyl derivatives; aliphatic and aromatic mercaptocarboxylicacids, mercaptodicarboxylic acids and aminomercaptocarboxylic acids,their N-alkyl, N-aryl and N-aralkyl derivatives or their N,N-dialkyl,N,N-diaryl or N,N-bis(aralkyl) derivatives, the esters of saidcarboxylic acids with aliphatic, aromatic or araliphatic alcohols;aromatic and aliphatic mercapto-alcohols and esters of themercaptoalcohols with C₁-C₁₀-alkanecarboxylic acids,C₆-C₂₀-aralkylcarboxylic acids or C₇-C₂₀-aralkylcarboxylic acids;mercaptodialkyl ketones; mercaptoalkyl aryl ketones; mercaptoalkyl- andmercaptoarylsulfonic acids and their alkali metal, alkaline earth metaland ammonium salts; thiourea which is unsubstituted or substituted onone or both nitrogen atoms by alkyl, aryl, aralkyl, alkylcarbonyl orarylcarbonyl; thiosemicarbazide which is unsubstituted or substituted onthe amine nitrogen by alkyl, aryl, aralkyl, alkylcarbonyl orarylcarbonyl; mercapto-substituted nitrogen heterocycles, includingmercapto-substituted imidazole, imidazoline, thiazole, thiazoline,triazole, thiadiazole and oxazole, which are unsubstituted orsubstituted by amino, halogen, alkyl or aryl and/or have a fused,unsubstituted or substituted benzene ring; aliphatic and aromaticthiocarboxylic acids and their amides, N-alkylamides and N-arylamides;mercaptoalkyltrialkoxysilanes.
 6. A process as claimed in claim 5,wherein the compound having at least one free thiol group is selectedfrom C₆-C₁₈-alkylmercaptans, 2-aminoethanethiol, N-methyl-,N,N-dimethyl-, N-ethyl- and N,N-diethyl-2-aminoethanethiol, 2-, 3- and4-aminothiophenol, 2-mercaptoacetic acid, 2-mercaptopropionic acid,2-mercaptoisobutyric acid, 2-mercaptosuccinic acid, 2-, 3- and4-mercaptobenzoic acid, 2-amino-3-mercapto-3-methylmethylbutanoic acid,the methyl, ethyl and phenyl esters of said carboxylic acids,2-hydroxyethanethiol, 2- and 3-hydroxypropanethiol, 2- and4-hydroxybutanethiol, 2-mercaptobutane-1,4-diol, a-thioglycerol,2-hydroxycyclopentanethiol, 2- and 4-mercaptophenol,2-mercaptoethanesulfonic acid, 2- and 3-mercaptopropanesulfonic acid, 2-and 4-mercaptobutanesulfonic acid and the alkali metal, alkaline earthmetal or ammonium salts of said sulfonic acids, 1-mercaptoacetone,phenacylthiol, 4-mercaptoacetophenone, 4-mercaptobenzophenone, thiourea,N-methyl-, N-ethyl-, N-alkyl-, N-acetyl- and N-phenylthiourea,N,N′-dimethyl-, N,N′-diethyl-, N,N′-diisopropyl-, N,N′-di-n-butyl- andN,N′-diphenylthiourea, thiosemicarbazide, 4-methyl-, 4-ethyl- and4-phenylthiosemicarbazide, mercaptothiadiazole,2-amino-5-mercaptothiadiazole, thiazoline-2-thiol, imidazoline-2-thiol,3-amino-5-mercaptotriazole, 2-mercaptobenzimidazole,2-mercaptobenzoxazole and 2-mercaptobenzothiazole, thioacetic acid,thiopropionic acid, thiobenzoic acid, thioacetamide, thiobenzamide,3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane. 7.A process as claimed in any of the preceding claims, wherein the stablefree radical or the source of stable free radicals is used in an amountof from 10-6 to 10 mol %, based on the molar amount of ethylenicallyunsaturated monomers.
 8. A process as claimed in any of the precedingclaims, wherein at least one free radical initiator is used forinitiating the polymerization and the molar ratio of stable freeradicals or source of stable free radicals to free radical initiators ischosen to be from 0.1 to
 10. 9. A process as claimed in any of thepreceding claims, wherein the polymerization temperature is from 40 to200° C.
 10. A process as claimed in any of the preceding claims, whereinthe stable radical is an N-oxyl radical and/or the free radical sourceis the source of an N-oxyl radical.